This invention relates to a method of and apparatus for automatic or semi-automatic welding or brazing of the type wherein a fillet-wire, mechanically fed to the point of welding on a work piece, is heated by a flame at the same time as the work piece is heated by the same flame, so that the wire is brought to its melting point, and wherein a short-circuit current passes between the fillet-wire and the work piece so that the Joule effect of the current heats the fillet wire.
In welding or brazing operations, the overall efficiency can be improved by using a short-circuit current through the fillet-wire to assist in heating the wire. The rate at which the wire melts to drop onto the work piece at the welding point is, in part, a function of the intensity of the short-circuit current. Also, the rate at which the fillet-wire is fed to the melting point affects the welding operation. For example, if the feed rate is too slow, the end portion of the wire may melt and detach and fall onto the weld, which is undesirable. Conversely, if the feed rate is too fast, the wire may not have sufficient time to melt; and, moreover, its end portion may undesirably bend when it contacts the work piece. Another disadvantage, which may arise if the feed rate is too slow, as aforementioned, or if the rate at which the molten metal melts is too high, such as by an excessive short-circuit current, is that when the end portion of the fillet-wire falls onto the work piece, an arc may occur therebetween. Such an arc may produce intense arc-light radiation and also, because of the energy of the arc, may impel molten metal, thus creating a hazardous condition. Accordingly, there is a need to maintain equilibrium between the feed rate and melting rate of the fillet-wire.
Furthermore, since many of the aforenoted disadvantages also may be produced if the surface of the work piece includes inequalities, it is desirable to maintain a uniform surface on the workpiece.